In recent years, reduction of carbon dioxide emission has been urgently required for the purpose of environment protection. The automobile industry is placing its hopes on the reduction of carbon dioxide emission by the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV) and is working on a motor-driven secondary battery that holds the key to the practical application of these vehicles. As shown in Patent Publication 1 below, attention has been paid on a layered bipolar battery as a secondary battery that can achieve a high energy density and a high output density.
A general bipolar battery includes a battery element in which a plurality of bipolar electrodes are serially connected or layered so as to sandwich an electrolyte layer, a packaging member that covers the entirety of the battery element to seal the battery element, and a terminal introduced from the packaging member to the outside in order to take out current. The bipolar electrode is structured so that one face of a collector includes a positive electrode active material layer to form a positive electrode and the other face includes a negative electrode active material layer to form a negative electrode. An electric cell layer is composed of a layered structure obtained by sequentially layering the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer. This electric cell layer is sandwiched between a pair of collectors. The bipolar battery is advantageous in that current flows in the battery element in a direction along which the bipolar electrode is layered (i.e., in the thickness direction of the battery) to provide a short current path to reduce current loss.
In order to obtain required capacity and voltage, a plurality of bipolar batteries are electrically connected to form a battery module or a plurality of battery modules are electrically connected to form an assembled battery. A battery module is one type of assembled battery including a plurality of electrically-connected bipolar batteries. In this specification, the term “battery module” is used to mean a unit to assemble an “assembled battery”.
Prior to the formation of a battery module, an operation is required in advance to use a packaging member to seal battery elements, thus preventing a series of operations for forming the battery module from being reduced. The series of operations for forming a battery module is also prevented from being reduced by another point that a plurality of bipolar batteries must be electrically connected to one another by mutually welding terminals introduced from a packaging member to the outside or must be connected via a connection member such as a bus bar. Another disadvantage of a deteriorated long-term reliability of a battery module is also caused when a battery module is installed in a vehicle such as an automobile or an electric train when compared with a case where the battery module is used in a stationary manner.
In view of the above, the present inventors have investigated the above disadvantages to find that the deteriorated long-term reliability of a battery module is caused by the following causing factors. Specifically, when the vibration from a road surface or a power source is applied to a battery module and is transmitted to the interior of the battery, an electron conduction path in the bipolar battery is deviated to cause the deteriorated long-term reliability of the battery module.
In order to solve this disadvantage, as described in Patent Publication 2 below, a battery module has been suggested that includes a flat-type battery in which current can be extracted from both surfaces in a direction along which an electric generation element is layered, a flat-plate-type electrode tab having a face contact with a current extracting face of the flat-type battery to extract current, and a packaging case covering the flat-type battery and the electrode tab. The inner face of the packaging case and the electrode tab sandwich an elastic member.
However, when the elastic member is provided between the inner face of the packaging case and the electrode tab with the use of a thick and rigid electrode tab for the bipolar battery, a significant influence is caused not only by the vibration entered through the battery packaging but also by the vibration entered through the electrode tab. Thus, there has been a requirement to further improve the resistance to the vibration entered through the electrode tab while reducing the series of operations for forming the battery module. Thus, the present inventors have further worked on this issue to suggest the invention of this application.
It is an objective of the present invention to provide a battery module that can be easily fabricated by reducing a series of manufacture operation, a low-cost assembled battery obtained by electrically connecting the battery modules, and a vehicle including these batteries.
It is another objective of the present invention to provide a battery module having a further-improved vibration resistance, a low-cost assembled battery obtained by electrically connecting the battery modules, and a vehicle including these batteries.    Patent Publication 1: Japanese Laid-Open Patent Publication No. 2001-236946    Patent Publication 2: Japanese Laid-Open Patent Publication No. 2002-110239